In a conventional mobile communication system, in an uplink from a mobile station UE to a radio base station Node B, a radio network controller RNC is configured to determine a transmission rate of a dedicated channel, in consideration of radio resources of the radio base station NodeB, an interference volume in an uplink, transmission power of the mobile station UE, transmission processing performance of the mobile station UE, a transmission rate required for an upper application, and the like, and to notify the determined transmission rate of the dedicated channel by a message of a layer-3 (Radio Resource Control Layer) to both of the mobile station UE and the radio base station Node B.
Here, the radio network controller RNC is provided at an upper level of the radio base station Node B, and is an apparatus configured to control the radio base station Node B and the mobile station UE.
In general, data communications often cause burst traffic compared with voice communications or TV communications. Therefore, it is preferable that a transmission rate of a channel used for the data communications is changed fast.
However, as shown in FIG. 1, the radio network controller RNC integrally controls a plurality of radio base stations Node B in general. Therefore, in the conventional mobile communication system, there has been a problem that it is difficult to perform fast control for changing of the transmission rate of channel (for example, per approximately 1 through 100 ms), due to processing load, processing delay, or the like.
In addition, in the conventional mobile communication system, there has been also a problem that costs for implementing an apparatus and for operating a network are substantially increased even if the fast control for changing of the transmission rate of the channel can be performed.
Therefore, in the conventional mobile communication system, control for changing of the transmission rate of the channel is generally performed on the order from a few hundred ms to a few seconds.
Accordingly, in the conventional mobile communication system, when burst data transmission is performed as shown in FIG. 2(a), the data are transmitted by accepting low-speed, high-delay, and low-transmission efficiency as shown in FIG. 2(b), or, as shown in FIG. 2(c), by reserving radio resources for high-speed communications to accept that radio bandwidth resources in an unoccupied state and hardware resources in the radio base station Node B are wasted.
It should be noted that both of the above-described radio bandwidth resources and hardware resources are applied to the vertical radio resources in FIGS. 2(a) and 2(c).
Therefore, the 3rd Generation Partnership Project (3GPP) and the 3rd Generation Partnership Project 2 (3GPP2), which are international standardization organizations of the third generation mobile communication system, have discussed a method for controlling radio resources at high speed in a layer-1 and a media access control (MAC) sub-layer (a layer-2) between the radio base station Node B and the mobile station UE, so as to utilize the radio resources effectively. Such discussions or discussed functions will be hereinafter referred to as “Enhanced Uplink (EUL)”.
Radio resource control methods that have been discussed in the “Enhanced Uplink” can be broadly categorized into three as follows. The radio resource control methods will be briefly described below.
First, a radio resource control method that is referred to as “Time & Rate Control” has been discussed.
In such a radio resource control method, a radio base station Node B determines a mobile station UE which can transmit user data and a transmission rate of user data of the mobile station UE per a predetermined timing, so as to signal information relating to a mobile station ID as well as the transmission rate of user data (or a maximum allowable transmission rate of user data).
The mobile station UE that is designated by the radio base station Node B transmits user data at the designated timing and the transmission rate (or within a range of the maximum allowable transmission rate).
Second, a radio resource control method that is referred to as “Rate Control per UE” has been discussed.
In such a radio resource control method, if there is user data that should be transmitted to the radio base station Node B, each mobile station UE can transmit the user data. However, the maximum allowable transmission rate of the user data, which is determined by the radio base station Node B and signaled to each mobile station UE for each transmission frame or each of a plurality of transmission frames, is used.
Here, when the maximum allowable transmission rate is signaled, the radio base station Node B signals the maximum allowable transmission rate itself, or a relative value thereof (for example, binary of an “Up command” and a “Down command”), at this timing.
Third, a radio resource control method that is referred to as “Rate Control per Cell” has been discussed.
In such a radio resource control method, a radio base station Node B signals a transmission rate of user data, which is common among mobile stations UE in communication, or information needed to calculate the transmission rate, and each mobile station UE determines a transmission rate of user data based on the received information.
Ideally, the “Time & Rate Control”, and the “Rate Control per UE” can be the best control methods for improving radio capacity in an uplink. However, a transmission rate of user data has to be granted after data volume stored in buffers of the mobile station UE, transmission power in the mobile station UE, or the like are grasped. Therefore, there has been a problem that control load is increased by the radio base station Node B.
In addition, in these radio resource control methods, there has been a problem that overhead becomes larger by exchanges of control signals.
On the other hand, in the “Rate Control per Cell”, there is an advantage in that control load by the radio base station Node B is small since the radio base station Node B signals information which is common in cells, and each mobile station UE autonomously seeks the transmission rate of user data based on the received information.
However, the radio base station Node B has to be configured in such a manner that the user data in the uplink from any mobile station UE can be received. Therefore, there has been a problem that an apparatus size of radio base station Node B becomes large to effectively utilize the radio capacity of the uplink.
Accordingly, there has been proposed, for example, a scheme (Autonomous ramping method) that the mobile station UE increases the transmission rate of user data from a pre-notified initial transmission rate in accordance with predetermined rules so that excessive allocation of radio capacity by the radio base station Node B can be prevented, thereby preventing increase of the apparatus size of radio base station Node B, as described in Non-patent Document 1.
In such a scheme, a radio base station Node B determines a maximum allowable transmission rate based on hardware resources and radio bandwidth resources (for example, an interference volume in an uplink) in each sector, so as to control the transmission rate of user data in communicating mobile stations UE. Detailed descriptions of a control scheme based on hardware resources and a control scheme based on an interference volume in an uplink will be given below.
In the control scheme based on the hardware resources, a radio base station Node B is configured to signal a maximum allowable transmission rate to a mobile station UE connected to a sector under the control thereof.
The radio base station Node B lowers the maximum allowable transmission rate so as to avoid shortage of the hardware resources when the transmission rate of user data in the mobile station UE connected to the sector under the control thereof is increased and the hardware resources are insufficient.
On the other hand, the radio base station Node B again increases the maximum allowable transmission rate when the space of the hardware resources become larger at a time of completion of user data transmission in the mobile station UE connected to the sector under the control thereof, or the like.
In addition, in the control scheme based on the interference volume in the uplink, a radio base station Node B is configured to signal a maximum allowable transmission rate to a mobile station UE connected to a sector under the control thereof.
When the transmission rate of user data in the mobile station UE connected to the sector under the control of a radio base station Node B increases and a measured interference volume (for example, a measured noise rise) in the uplink exceeds an allowable value (for example, a maximum allowable noise rise), the radio base station Node B lowers the maximum allowable transmission rate so that the interference volume in the uplink can be within a range of the allowable value (see, FIG. 3).
On the other hand, when the interference volume (for example, the noise rise) in the uplink is within a range of the allowable value (for example, the maximum allowable noise rise), thereby having a space, at the time of completion of user data transmission in the mobile station UE connected to the sector under the control of the radio base station Node B, or the like, the radio base station Node B again increases the maximum allowable transmission rate (see, FIG. 3).
As for the enhanced uplink, there exists a concept of a serving cell (or a serving cell set). FIG. 4 shows an example of a channel connection configuration in the mobile communication system to which enhanced uplink is applied.
Here, in terms of the enhanced uplink, a channel for transmitting user data by using the HARQ processing or the scheduling processing is defined as an Enhanced Dedicated Physical Channel (E-DPCH). A channel for transmitting uplink user data is defined as an Enhanced Dedicated Physical Data Channel (E-DPDCH), and a channel for transmitting uplink control data is defined as an Enhanced Dedicated Physical Control Channel (E-DPCCH).
In the mobile communication system, not only the E-DPCH but also a conventional Dedicated Physical Channel (DPCH) is also transmitted. It is assumed that control information on a layer 3 between the core network and the mobile station UE is transmitted on the DPCH.
In addition, in the mobile communication system, an Absolute Grant Channel (AGCH) transmits the maximum allowable transmission rate of the uplink user data.
The mobile station UE always receives the absolute grant channel (AGCH) that is always transmitted from only one cell. Here, a cell transmitting the AGCH that the mobile station UE should receive is called a “serving cell” of the mobile station UE, and cells belonging to the same radio base station NodeB as the serving cell are called a “serving cell set” of the mobile station UE.
Since the serving cell controls the transmission rate of the uplink user data in the mobile station UE, the radio network controller RNC generally takes control such that a cell having the strongest electric field strength in downlink or uplink would become a serving cell. Here, it is called “serving cell change” that a serving cell of a mobile station is changed.
In the conventional mobile communication system, when resources suitable for the transmission rate of user data transmitted from the mobile station UE which performs the cell change are not allocated to a destination cell in the cell change, the cell change is not performed smoothly.
Accordingly, in such case, the destination cell lowers the signaled maximum allowable transmission rate to have some margin in the resources, and the resources are secured for the mobile station UE. However, there is a problem that all the user data that have been transmitted by that time may be received as errors.
More specifically, in the conventional mobile communication system, there is a problem that significant deterioration in communication quality may occur, since the radio base station NodeB including the destination cell in the cell change cannot allocate the resources to the mobile station in which the cell change is to be performed.    (Non-patent Document 1) 3GPP TSG-RAN R1-040773